Multitube mosaic reso-jet motor



1951 J. Y. DUNBAR ET AL I MULTITUBE MOSAIC RESO-JET MOTOR Filed July 30, 1945 1 ,5 Wm Y m DONALD L HERR Patented Nov. 6, 1951 MULTITUBE MOSAIC RESO-J ET MOTOR James Y. Dunbar and Donald L. Herr, United States Navy Application July 30, 1945, Serial No. 607,894

(Granted under the act of March 3, 1883, as amended April 30, 1928; 370 0. G. 757) 4 Claims.

This invention relates to improvements in'resojet motors.

An object of this invention is to provide a resojet motor with improved specific thrust or efficiency.

Another object of this invention is to provide a reso-jet motor that will have an improved. resonance.

Other objects and advantages of this invention will become apparent as the discussion proceeds and is considered in connection with the accompanying claims and drawing wherein like characters of reference designate like parts in the several views and wherein:

Fig. l is a plan piew of a plurality of single resojet motors grouped into a single mosaic unit as embodied in this invention;

Fig. 2 is an end View of a plurality of single resojet motors grouped into one mosaic unit as embodied in this invention;

Fig. 3 is a cut-away plan view of a reso-jet motor embodying a modification of this invention; 1

Fig. 4 is a perspective view of a reso-jet motor carrying a semi-infinite bafile as embodied in a further modification of this invention, and

Fig. 5 is a partial sectional view of the reed valves which may be used for controlling the intake, taken on the line 5-5 of Fig. 2.

Before proceeding with the detailed description of this invention, it is necessary to define certain hereinafter used terms. The term reso-jet, as used throughout this specification, shall broadly refer to any type of jet motor working on pulsating or cyclically firing principle of a combustion mixture taking place in any cylinder, chamber, tube or the like, regardless of shape or length or the combination thereof, restricted at one end and open at the other. Suction for introducing a charge of air for the explosion and compression for increasing the firing of the combined fuel and air mixture in the chamber are obtained as a result of the natural oscillation of the gas mass in the tail pipe. Air supporting combustion is drawn from the atmosphere through the restricted end of the motor. Intake control for the air may be by designed acoustical inertance or by valves, of the reed, resilient, rotating, or reciprocating type. Combustion of the mixed-rfuel and air may take place, either from an auxiliary source such as an electric spark plug, or internally from the heat or tail flame of the proceding charge. The term mosaic will be used throughout this specification to designate the grouping of a plurality of single reso-jet units into a combined single unit, so that there is a matched coupling impedance from one unit to one or more'of the other units. The specific geometric configuration into which the single motor units are combined is not considered essential in the use of the term for the purpose of this specification. However, broadly considered, the word mosaic, hereinafter used, refers to the grouping of single reso-jet units into a geometric pattern as illustrated in Figs. 1 and 2, but it is to be understood that the term likewise includes any other grouping of these units in anyform desired so long as the functions described below are accomplished.

Referring now to the drawing, wherein for the purpose of illustration, is shown a preferred embodime'nt of this invention, the numeral 5 designates the explosion chamber of a conventional reso-jet motor. The numeral 1 designates the conventional tail pipe having an opening 3. Air intake control means 8 either of a designed acoustical inertance or valves of the reed, resilient, rotary or reciprocating type,'may be affixed to the end of the explosion chamber 6 and provide for the entrance of air into the said cham ber. In the present embodiment of the invention resilient valves are illustrated. Fuel is injected by the conventional nozzle (not. shown). A plurality of single unit motors, in a mosaic, is affixed together, as shown in Figs. 1 and 2, in any suitable manner such as by welding or the like. It is to be noted, as disclosed in the views shown in Figs. 1 and 2, that the tail pipes are disposed inwardly at their ends 8, so that they are tangent, eachwith the other at Ill as shown. The combustion chambers 6 likewise are tangent, each with the other at H, as shown. The specific geometrical configuration of the mosaic of the combined motor units may take any one of several forms without departing from the spirit of this invention. The mosaic may be circular, as shown in Fig. 2,; or may be; square, rectangular, etc, as long as themosaicof the combined unitis such that there. is; a pressure reactionat: the

nozzles from one unit to one or more of the other units.

In the modification shown in Fig. 3, the numeral l2 designates a conventional combustion chamber of a reso-jet motor having an air intake l3 at one end, as shown. In place of the conventional single unit tail pipe for each combustion chamber, as shown in Fig. 1, a plurality of tail pipes M are affixed to the combustion chamber I2, as shown.

In the modification shown in Fig. 4, a semiinfinite bafile plate l5, specific configurations of which will vary in accordance with the specific design of any single unit motor or mosaic grouping of single units into one combined motor, but generally taking the form of a surface of revolution or translation extending from the perimeter of the mosaic, is affixed in any suitable manner such as by welding or the like, to the ends of the tail pipe or pipes l, as shown. By proper design of the curvature of the generatrix of such surface in accordance with the frequency and size of the mosaic used, as may be determined by trial, an increase in the compression in the units may be obtained so as to increase their efliciency.

In operation, the reso-jet motor embodied in this invention performs as follows:

Air is taken into the combustion chamber 6 through the valves 9 in each of the units, and fuel is injected through nozzles into the said chamber. Initial firing of this charge is accomplished by an electrical spark (not shown) in the combustion chamber 6 in the conventional manner. The hot gases of combustion having expanded, escapement thereof occurs through the tail pipe '1. Each reso-jet unit, in the mosaic, is tuned to oscillate at a given fundamental frequency, which is designed to be the same for each unit, before being assembled in the mosaic, so that as each unit fires, due to the fundamental frequency at which each motor is tuned, the exploding gases will move within the chamber and tail pipe at the fundamental frequency at which the unit is tuned.

The escape of these gases at high velocity provides that thrust by reason of jet reaction. At resonance, the maximum pressure variation above and below the ambient or average pressure in the chamber is obtained. During the low pressure part of the resonant cycle in the combustion chamber, fuel and air are drawn in, burned to raise the pressure and eject gases in the jet, causing the cycle to be maintained.

Partial compression for the succeeding explosion within the chamber is provided by the inertia of gases in the tail pipe induced to move toward the chamber by the low pressure phase of the cycle. By reason of the mosaic grouping or proximate spacing of the jets, as disclosed by this invention, in relation to each other, all units of the group are forced to act synchronously in resonance, or in phase with each other, by reason of their mutual influence This effect will be readily understood when it is recalled that in the operation of a single reso-jet motor, an explosion in the combustion chamber closes the inlet valves, and the exhaust gas out of the exhaust vent gives the motor a propelling thrust. The exhaust also creates a partial vacuum in the chamber, so that pressure of the outside air causes the valves to reopen, and the chamber is again filled with air or explosive mixture to form another explosion. It follows then, that any external condition which influences the pressure condition in the combustion chamber, or impedes the ebb and flow of gases therein as governed by the laws of acoustics, is going to influence the frequency of operation. It is apparent then, that if other similar reso-jet motors are placed adjacent the first one with their exhaust vents near the vent of the first, that gas pressure from the exhausts of the others is going to be exerted on the gas in the first, since the expanding gases from the others exert some pressure in all directions. If it is recalled that a pressure wave is travelling back and forth along thelength of the combustion chamber, this periodic pressure wave clearly will be influenced by other pressures exerted at the exhaust vent. It is well known in the electrical art, for example, that two coupled oscillators oscillating at slightly different frequencies tend to pull .together and synchronize their oscillations. An analogous effect is noted when two or more similar reso-jet motors have their exhaust vents grouped in a mosaic pattern. Further, by using a multiplicity of units with a common frequency for all units, the dimensions of the jet area may be increased to give a more efiicient thrust value for each unit without appreciably changing the operating frequency of the total assembly in the mosaic, because the pressure variation above and below ambient or average pressure for such unit is increased by the mutual or coupling impedance between adjacent units. This is due to the effect of the pressure pulse from an adjacent unit aiding in raising the pressure of the return wave in any unit during its compression cycle. This effect is readily understood when it is recalled that the pressure wave which travels down the exhaust passage following the explosion is reflected back from the vent. If the wave is reinforced at the vent by small portions of the pressures obtained from the vents of other motors resulting from their simultaneous exhausts, the reflected wave will accordingly be greater.

It is necessary that each unit of the group be designed to operate at about the same fundamental frequency. However, even though the frequencies of the several motor units are the same, if there were no influence of one acting on another as in the mosaic embodied in this invention, there would be a random phase relation between the units. The operating of single units in a mosaic, as disclosed by this invention, will keep all of the said units in phase, thereby keeping the overall efliciency of the mosaic motor higher, because as one unit starts to get out of phase" it will be brought back into phase by the mutual influence of the coupling impedance of the other adjacent units in the mosaic, the coupling being provided by the interaction of the exhaust gases.

By firing the several individual units separately or in banks, directional control and throttling may be obtained.

The fundamental operation of the modification shown in Fig. 3 is substantially the same as the operation described above. The resonance of each of the tail pipes I4 is influenced by the resonance of the surrounding tail pipes, thus keeping all tail pipes synchronized. Also, the wave front of each tail pipe, giving an increased impedance to the tail pipes adjacent thereto, builds up a greater compression in the firing chamber l2, just as in the multiple motor mosaics.

The conception of this invention, in a general sense, is that n reso-jet units within certain limits, in mosaic, will produce more than n times the thrust obtainedrwith a single reso jet" motor operating separately for the same unit fuel rate a per jet as a-result of the increased compressionga nd as a result of the more. favorable ratio or combustion chamber area to wavelength;

coupling impedance per unit area of said; mjosa-ic,

or such dimension secured by g rouping a number of'jet motors which gives the greatest increase of single jet efficiency consistent with the mosaic economy. It is likewise to be noted that the impedance at the ends of the tail pipes in mosaic for a given designed frequency of a single reso-jet unit is a distinct funtion of the area of the mosaic of the tail pipes.

A further increase in compression in the resojet motor can be accomplished by adapting the semi-infinite baffle shown in Fig 4 to the ends of the tail pipe. The improved compression from the baffle is given to the reso-jet motor by further increasing the impendance of the wave front as it leaves the tail pipe and causing a greater portion of the pressure caused by the expanding gas from any one vent to be exerted toward the other vents.

As is known in the acoustic art, a transducer operating in air has its lowest efficiency when its effective piston area is small in relation to its wavelength. In a jet motor, the larger the tail pipe diameter is made to increase its area, the lower becomes its resonant frequency and hence the longer the wavelength. So that in the construction of reso-jet motors, optimum efficiency can not be obtained by increasing the tail pipe diameter.

The mosaic pattern of the instant invention maintains the frequency and wavelength of a single reso-jet motor of small diameter, but greatly increases the effective piston, or combus tion chamber, area by grouping a number of jet motors together, operating simultaneously. Each jet motor is designed to have effectively the same natural frequency, and when a number of such devices are operating contiguously and simultaneously they are held in phase without mechanical connections. If one of the devices of the group tends to drop out of phase, it will be brought back intov phase by the coupling effect of the gas mass motion common to the mosaic assembly of the tail pipe area. The coupling is acoustical. By such means the effective area (or diameter) of the mosaic approaches the wave length of operation, with increased efficiency; so that the thrust of a group of n jet motors is greater than n times the thrust of a single reso-jet motor taken alone.

It is to be understood that the form of our invention, herewith shown and described, is to be taken as a preferred example of the same, and that various changes in the shape, size and arrangement of parts may be resorted to, without departing from the spirit of our invention, or the scope of the subjoined claims.

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

1. In jet motor apparatus of the type wherein a plurality of similar pulsing jet motors of small cross-section are mounted in contiguous relationship and synchronized to operate in phase to provide an arrangement in whichan optimum ratio of area to. wavelength: is maintained, the improvement'which consists in utilizing a plurality of"reso-ujet motors, each of said reso-jet motors having substantially the same natural resonant frequency of-op'erat-ion based upon the dimensisnstherect the; tailpip s; of said rem-let motors terminating in substantially a common plane substantially transvere to the axis of thrust, the gases from said tailpipes" interacting and maintaining said reso-jet motors in synchronisfrnwithout the use of mechanical controls.

2. ln-jet motor-apparatusof the type wherein a plurality of similar pulsing jet motors of small cross-section are mounted in contiguous relationship and synchronized to operate in phase to provide an arrangement in which an optimum ratio of area to wavelength is maintained, the improvement which consists in utilizing a plurality of reso-jet motors, each of said reso-jet motors having substantially the same natural resonant frequency of operation based upon the dimensions thereof, the tailpipes of said reso-jet motors terminating substantially in a common plane substantially transverse to the axis of thrust, the exhaust gases providing coupling between said reso-jet motors, said coupling maintaining said reso-jet motors in synchronism without the use of mechanical controls.

3. In jet motor apparatus of the type wherein a plurality of similar pulsing jet motors of small cross-section are mounted in contiguous relationship and synchronized to operate in phase to provide an arrangement in which an optimum ratio of area to wavelength is maintained, the improvement which consists in utilizing a plurality of reso-jet motors, each of said motors having substantially the same natural resonant frequency of operation based upon the dimensions thereof, the tailpipes of said reso-jet motors terminating substantially in a common plane substantially transverse to the axis of thrust, the exhaust gases providing coupling between said reso-jet motors, said coupling maintaining said reso-jet motors in synchronism without the use of mechanical controls, and bafile means affixed to said plurality of reso-jets near the tailpipes thereof for maintaining the degree of coupling therebetween at a predetermined value.

4. In jet motor apparatus of the type wherein a plurality of similar pulsing jet motors of small cross-section are mounted in contiguous relationship as a unit and synchronized to operate in phase to provide an arrangement in which an optimum ratio of area to wavelength is maintained, the improvement which consists in utilizing a plurality of reso-jet motors, each of said reso-jet motors including means forming a combustion chamber having an exhaust tailpipe, said combustion chambers having substantially the same natural resonant frequency for a preselected period of operation of the motors determined by the speed of sound in the hot gases of the chambers, the tailpipes of said reso-jet motors terminating in a unit substantially in a common plane substantially transverse to the axis of thrust, the exhaust gases of any one motor unit exerting a pressure on adjacent tailpipes to provide coupling between said reso-jet motors and maintaining them in synchronism without the use of mechanical connections between the reso-jet motors, and a baflle affixed to the outer periphery of said tailpipe unit and adapted to provide an increased impedance to the wave front of said exhaust tailpipes thereby increas Number ing the coupling between the reso-jet motors. 1,983,405 JAMES Y. DUNBAR. 2,086,101 DONALD L. HERR. 2,283,863 5 2,297,425 REFERENCES CITED 2,427,345 The following references are of record in the 2,432,359 file of this patent:

UNITED STATES PATENTS 10 Number Number Name Date 188,642 617,753 Le Pontois Jan. 17, 1899 548,898

1,405,482 Bostedo Feb. 7, 1922 Name Date Schmidt Dec. 4, 1934 stoller July 6, 1937 Achterman May 19, 1042 Meissner Sept. 29, 1942 Forsyth Sept. 23, 1947 Streid Dec. 9, 1947 FOREIGN PATENTS Country Date Great Britain Nov. 29, 1923 Great Britain Oct. 28, 1942 

